gas lock front sight height

T

twoguntim

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Why does SEI make two different gas lock front sights, one for an 18 inch barrel, and the other for a 22 inch? Since the distance between the front and rear sight does not change, why make two models?
 
Thomas answered this before. And while the distance doesn't change the different length barrels does change things. I'll see if I can dig it up as I'd screw up the explanation.

Found it:

No worries man it stumps most guys at first and I've scratched my own head over the issue more times than one hehehehe

If you put it on paper, it goes like this.
Draw a straight line representing the bore center of a 22" barrel. The line must be the length of the distance between rear sight aperture and front sight blade at it's highest point.
Next take the height of the center of the bottomed out rear aperture and make a mark.
Now go to front sight location, measure up from the line, the distance from bore center to top of standard sight blade.
Connect the two marks with a straight line.

This will show you why a higher sight is needed as the two lines before you will not be parallel. The top (sight) line angles down, towards the bore. So as you move the sight back, the blade height must increase to compensate.

This is magnified when shortening the barrel as you now must also account for the change in tragectory that 3 1/2 less inches of barrel gives the .308 cartridge. Again, an increase in blade height in necessary.
Click to expand...
 
I have never heard of this being an issue when building an AR, or any other platform, so why would 3.5 inches matter with a M14?
 
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